Do you know what a black hole is? A:

A black hole is a super-dense planet. It absorbs everything, and light can't escape. Now some scientists have analyzed that there is no black hole in the universe, which needs further proof, but we can have different opinions academically. )

Black holes have great gravity, and even light is attracted by them and cannot escape. There is a huge gravitational field hidden in a black hole, and the gravity is so great that nothing, even light, can escape from the palm of the black hole. Black holes don't let anything in their boundaries be seen by the outside world, which is why such objects are called "black holes". We can't observe it through the reflection of light, and we can only indirectly understand the black hole through the objects around us that are affected by it. Having said that, a black hole still has its boundary, that is, the "horizon". It is speculated that the black hole is the remnant of the death star, which was produced when a special massive Supergiant star collapsed. In addition, stars with mass greater than Chandrasekhar's limit will definitely form black holes in the final stage of evolution, while stars with mass less than Chandrasekhar's limit cannot form black holes. (belt)

■ Interpretation of physical viewpoints

A black hole is actually a planet (similar to a planet), but its density is very, very high. Objects close to it will be bound by its gravity (just like people on earth will not fly away), and no matter how fast they use it, they can't escape. For the earth, flying at the speed of the second universe (1 1.2km/s) can escape from the earth, but for a black hole, its speed of the second universe exceeds the speed of light, so even light can't escape, so the incoming light is not reflected, and our eyes can't see anything except black.

Black hole dynamics

In order to understand the dynamics of black holes and how they prevent everything inside from escaping from the boundary, we need to discuss general relativity.

■ relativity of general relativity

General relativity is a theory of gravity founded by Einstein, which is applicable to planets, stars and "black holes". This theory put forward by Einstein in 19 16 shows how space and time are distorted by the existence of massive objects. In short, general relativity says that matter will bend space, and the bending of space will in turn affect the motion of objects passing through space.

Let's see how Einstein's model works. First of all, consider that time (the three dimensions of space are length, width and height) is the fourth dimension in the real world (although it is difficult to draw another direction other than the usual three directions, you can try to imagine it). Secondly, consider that time and space is the bed surface of a huge taut spring bed for gymnastics performance.

Einstein's theory holds that mass bends time and space. We might as well put a big stone on the bed surface of the spring bed to illustrate this scene: the weight of the stone makes the tight bed surface sink a little. Although the surface of the spring bed is basically flat, its center is still slightly concave. If more stones are placed in the center of the spring bed, it will have a greater effect and make the bed surface sink more. In fact, the more stones there are, the more the spring bed surface bends.

Similarly, massive objects in the universe will distort the structure of the universe. Just as 10 stone can bend the spring bed better than 1 stone, celestial bodies with much greater mass than the sun can bend space better than celestial bodies with mass equal to or less than one sun.

If a tennis ball rolls on a tight spring bed, it will move in a straight line. On the contrary, if it passes through a concave place, its path is arc. Similarly, celestial bodies will continue to move in a straight line when crossing the flat area of time and space, while celestial bodies crossing the curved area will move in a curved trajectory.

Now let's look at the influence of black holes on the surrounding space-time areas. Imagine putting a very heavy stone on a spring bed to represent a very dense black hole. Stones will naturally have a great influence on the bed surface, which will not only bend and sink its surface, but also cause the bed surface to break. A similar situation can also happen in the universe. If there is a black hole in the universe, the cosmic structure there will be torn apart. The rupture of this spatiotemporal structure is called singularity or spatiotemporal singularity.

Now let's see why nothing can escape from a black hole. Just as a tennis ball rolls over a spring bed and falls into a deep hole formed by a big stone, an object passing through a black hole will be caught by its gravity trap. Moreover, saving unlucky objects requires infinite energy.

As we have said, nothing can enter a black hole and escape from it. But scientists believe that black holes will slowly release energy. Hawking, a famous British physicist, proved in 1974 that a black hole has a non-zero temperature, and the temperature is higher than its surroundings. According to the principle of physics, all objects whose temperature is higher than the surrounding environment will release heat, and black holes are no exception. A black hole will emit millions of trillion years of energy, and the energy released by a black hole is called "Hawking radiation". When a black hole dissipates all its energy, it will disappear.

Black holes between time and space slow down time, make space elastic, and devour everything that passes through it. 1969, American physicist John? Artie. Wheeler named this insatiable space "black hole".

We all know that a black hole is invisible because it can't reflect light. In our minds, black holes may be distant and dark. But Hawking, a famous British physicist, believes that black holes are not as black as most people think. Through the observation of scientists, there is radiation around the black hole, and it is likely to come from the black hole, which means that the black hole may not be as black as imagined. Hawking pointed out that the radioactive material source of black holes is a kind of solid particles, which are produced in pairs in space and do not follow the usual physical laws. Moreover, after these particles collide, some will disappear into the vast space. Generally speaking, we may not have a chance to see these particles before they disappear.

Hawking also pointed out that when black holes are produced, real particles will appear in pairs accordingly. One of the real particles will be sucked into the black hole, the other will escape, and a bunch of escaped real particles will look like photons. For the observer, seeing the escaping real particles is like seeing the light from a black hole.

Therefore, to quote Hawking's words, "A black hole is not as black as it is supposed to be", it actually emits a lot of photons.

According to Einstein's law of conservation of energy and mass. When an object loses energy, it also loses mass. Black holes also obey the law of conservation of energy and mass. When a black hole loses energy, it doesn't exist. Hawking predicted that the moment the black hole disappeared, there would be a violent explosion, releasing the energy equivalent to millions of hydrogen bombs.

But don't look up with anticipation, thinking that you will see the fireworks show. In fact, after the black hole explodes, the energy released is very large, which is likely to be harmful to the body. Moreover, the energy release time is also very long, some of which will exceed 10 billion years to 20 billion years, which is longer than the history of our universe, and it will take trillions of years for the energy to dissipate completely.

It is easy to imagine a "black hole" as a "big black hole", but it is not. The so-called "black hole" is such a celestial body: its gravitational field is so strong that even light cannot escape.

According to the general theory of relativity, the gravitational field will bend space-time. When the star is large, its gravitational field has little influence on time and space, and the light emitted from a certain point on the surface of the star can be emitted in any direction in a straight line. The smaller the radius of the star, the greater the bending effect on the surrounding space-time, and the light emitted at some angles will return to the surface of the star along the curved space.

When the radius of a star is less than a certain value (called "schwarzschild radius" in astronomy), it will even capture the light emitted from the vertical plane. At this time, the star becomes a black hole. To say it is "black" means that once anything falls in, it can't escape, including light. In fact, black holes are really invisible.

The creation of black holes

The process of a black hole is similar to that of a neutron star. The core of a star shrinks rapidly and explodes violently under its own weight. When all the substances in the core become neutrons, the contraction process stops immediately and is compressed into a dense planet. But in the case of a black hole, because the mass of the star core is so great that the contraction process goes on endlessly, the neutron itself is ground into powder under the attraction of the squeezing gravity itself, and the rest is the matter with unimaginable density. Anything near it will be sucked in, and the black hole will become like a vacuum cleaner.

Like white dwarfs and neutron stars, black holes probably evolved from stars with a mass more than 20 times that of the sun.

When a star ages, its thermonuclear reaction has exhausted the fuel (hydrogen) in the center, and the energy generated by the center is running out. In this way, it no longer has enough strength to bear the huge weight of the shell. Therefore, under the heavy pressure of the shell, the core began to collapse, until finally a small and dense star was formed, which could balance the pressure again.

Stars with smaller mass mainly evolve into white dwarfs, while stars with larger mass may form neutron stars. According to scientists' calculations, the total mass of neutron stars cannot be more than three times that of the sun. If it exceeds this value, there will be no force to compete with its own gravity, which will lead to another big collapse.

This time, according to scientists' guesses, matter will move relentlessly towards the center point until it becomes a small volume and tends to be very dense. When its radius shrinks to a certain extent (it must be smaller than that of schwarzschild radius), as we mentioned above, the huge gravity makes it impossible to shoot out even light, thus cutting off all the connection between the star and the outside world-a "black hole" is born.

According to scientists' calculations, if the speed of an object is 7.9 kilometers per second, it can circle the earth in the air without being pulled back to the ground by the gravity of the earth. This speed is called the first cosmic speed. If you want to get rid of the bondage of the earth's gravity completely, you must have at least a speed of 1 1.2km/s, which is the so-called second cosmic speed. But for other celestial bodies, the speed needed to escape from its surface is not necessarily so great. The greater the mass and the smaller the radius of a celestial body, the harder it is to get rid of its gravity, and the greater the speed required to get rid of it.

According to this truth, we can think that there may be a celestial body with a large mass and a small radius, which makes it escape at the speed of light. In other words, the gravity of this celestial body is so strong that even the light of 300,000 kilometers per second is held by its gravity and cannot run out. Since the light of this celestial body can't escape, we can't see it when we speak, so it is black. Light is the fastest in the universe, and nothing can move faster than the speed of light. Since light can't escape from this celestial body, of course, other substances can't escape. As long as everything is sucked in, it will never come out, just like falling into a bottomless pit. This is a celestial body and people call it a black hole.

We know that the radius of the sun is 700,000 kilometers now. If it becomes a black hole, the radius will be greatly reduced. To what extent? It can only be three kilometers. The earth is more pitiful. Its radius has now exceeded 6000 kilometers. If it becomes a black hole, the radius will be reduced to only a few millimeters. There will be such a big compressor, which can shrink the sun and the earth so much! It's like a fairy tale in a movie, a black hole, so bizarre. However, the above is not imaginary, but based on strict scientific theory. It turns out that black holes are also transformed from stars in their later years, like relatively small stars, which will become white dwarfs in their later years; Neutron stars will form when the mass is relatively large. Now let's add that stars with greater mass will eventually become black holes in their later years. Therefore, to sum up, white dwarf neutron stars and black holes are the results of three changes in the stars in their later years.

Now, the white dwarf is found, the neutron star is found, and the black hole is found? We should also find them. Mainly because black holes are black and really hard to find. Especially those single black holes, there is nothing we can do now. There is a situation where it is easier to find black holes, that is, black holes in binary stars.

A binary star is two stars orbiting each other. Although we can't see the black hole, we can analyze the movement route of the visible stars. What is the reason? Because every star in a binary star moves along an elliptical path, but a single star does not move like this. If we see a star moving along an elliptical route in the sky, but we can't see its companion, it is worth studying carefully. We can measure the size of the ellipse that a star walks through and the time it takes to complete a week. With these, we can calculate the mass of the invisible' companion'. If the calculated mass is very large, which exceeds the mass that a neutron star can have, it can be further proved that it is a black hole.

In Cygnus, there is a pair of binary stars named Cygnus X- 1. One of these binary stars is a visible bright star, but the other is invisible. According to the movement route of the bright star, it can be inferred that its' companion star' mass is very large, at least five times that of the sun. Such a large mass is impossible for any neutron star. Of course, there are other evidences besides these. Therefore, it can be basically determined that the invisible celestial body in Cygnus X- 1 is a black hole. This is the first black hole discovered by human beings.

In addition, several pairs of binary stars are similar to Cygnus X- 1, and there may be black holes in them. Scientists are doing further research on them. It is easy to imagine a "black hole" as a "big black hole", but it is not. The so-called "black hole" is such a celestial body: its gravitational field is so strong that even light cannot escape.